1. Field of the Invention
The present invention relates to metastasis inducing DNA's, a method of identifying such DNA's, and their use in diagnosis and therapy.
2. Description of Related Art
Most cancers are thought to be due to alterations in specific genes caused either by mutation making their gene-product in some way more effective or by over expression of a normal gene giving an enhanced effect. These oncogenes have largely been identified by introducing gene-length fragments of DNA from human cancers into a mouse fibroblast cell line, in culture, and selecting those cell lines that grow in an uncontrolled manner in liquid or semi-solid medium. The oncogenes themselves have been isolated by cloning the human DNA fragments away from the mouse DNA by standard recombinatorial techniques. Alternatively mutations can arise in genes that suppress their own activity such as, for example, p53 or Rb or which suppress the levels of their products such as, for example NM-23. These are referred to as tumour suppressor oncogenes. In the commonly-occurring cancers, it is believed that between 5 and 7 such changes in oncogenes or tumour suppressor oncogenes are required to produce a full-blown cancer.
WO 86/03226 discloses a method for detecting a discrete, transmissible mammalian gene associated with tumour metastasis. The method uses a non-syngeneic system. The teaching was later retracted—Proc Nat. Acad. Sci USA, 1988, 85 5581.
WO 94/28129 identifies a tumour metastasis gene of 2858 base pairs which codes for a protein which is expressed in malignant human tumours and their metastasis. The method used to identify it used a non-syngeneic system employing nude (defective) mice.
Cancer research 54, 2785-2793 (1994) is a paper by the applicants. It discloses a method for showing the presence of metastasis inducing DNA. No disclosure is, however, made of how to recover the sequences for identification.
Cancer research 54 832-837 (1994) is a paper suggesting that antisense OPN DNA expression was associated with reduced tumorigenicity of these cells in the flanks and in lungs. The paper does not measure or investigate metastasis as such.
EP 0607054 disclosures a process for constructing a cDNA library. It described a method, using linkers and PCR for identifying signal peptides. The application is not to metastasis at all and the approach uses expression vectors for detection.
The major forms of cancer, including breast cancer, lung cancer and colonic cancer cannot be cured effectively because, although the current therapies may be effective against the primary tumours, they are largely ineffective against the disseminating or metastasizing cells, which ultimately kill the patient. Despite the enormous effort in cancer research very little is known at the molecular level about the most important life-threatening process, that of metastasis. Most of the oncogenes and suppressor oncogenes that have been discovered have been found from their ability to promote uncontrolled growth of the mouse fibroblast cell line. The major problem in this field is that determining cell growth does not give a measure of the process of metastasis. In fact, although uncontrolled growth is an important aspect of the initial events in the development of a cancer, the rate of growth of distant metastases can be remarkably slow. Hence the process of metastasis is largely independent of processes involving cell-growth, except in its final phases. Therefore, it is unlikely that oncogenes and tumour suppressor oncogenes will have much involvement in the process of metastasis and be useful diagnostic or therapeutic targets for control and elimination of metastatic disease.